<b>Screening of a potential probiotic</b><b><i> Lactiplantibacillus plantarum</i></b><b> NUC08 </b><b>and its synergistic effects with yogurt starter</b>

This study aims to identify lactic acid bacteria (LAB) isolates possessing physiological characteristics suitable for use as probiotics in yogurt fermentation. Following acid and bile salt tolerance tests, <i>Lactiplantibacillus</i><i> plantarum </i>(NUC08 and NUC101), <i>Lacticaseibacillus rhamnosus</i><i> </i>(NUC55 and NUC201), and <i>Lacticaseibacillus</i><i> paracasei </i>(NUC159, NUC216 and NUC351) were shortlisted based on intraspecies distribution for further evaluation. Their physiological probiotic properties, including transit tolerance, adhesion, auto-aggregation, surface hydrophobicity, biofilm formation, and antibacterial activity, were assessed. Principal Component Analysis (PCA) indicated that<i> L. plantarum </i>NUC08 was the preferred choice among the evaluated strains. Subsequent investigations revealed that co-culturing <i>L. plantarum</i> NUC08 with two yogurt starter strains resulted in a cooperative and synergistic effect, enhancing the growth of mixed strains and increasing their tolerance to simulated gastric and intestinal conditions. Additionally, when <i>Vibrio harveyi </i>bioluminescent reporter strain was used, the three co-cultured strains cooperated to induce the activity of a quorum sensing (QS) molecule AI-2, hinting a potential connection between phenotypic traits and QS in the co-cultured strains. Importantly, LAB viable counts were significantly higher in yogurt co-fermented with <i>L. plantarum</i> NUC08, consistently throughout the storage period. In conclusion, the study demonstrates that the probiotic strain <i>L. plantarum </i>NUC08 can be employed in synergy with yogurt starter strains, affirming its potential for use in the development of functional fermented dairy products.